This disclosure is directed to a system for sampling gas discharges from a vent, blow down, flare or smoke stack. While smoke, vent, blow down or flare stacks can be small, they typically discharge large quantities of gases to atmosphere. Large sized stacks can easily discharge several thousand tons of effluent gases per day. The chemical content of the discharge gives rise to air pollution problems, including acid rain. A smoke, vent, blow down or flare stack discharge is normally resultant of a furnace, smelter operation or gas operation in which fossil fuels are converted into combustion produces discharged through the stack. In an ideal combustion situation, the fossil fuel materials are converted into H.sub.2 O and CO.sub.2 to thereby provide a discharge which is substantially clear and free of undesirable chemical products. In a smelter operation, ores may be processed with exposure to heat and might possibly discharge other gaseous products including SO.sub.x, CO, and other partially or totally oxidized elements. One gas example is NO.sub.x. The quantities of gas discharges become important from the point of view of controlling and limiting certain discharges. For instance, enhanced after-burning can be incorporated to reduce CO discharge. Scrubbing can be incorporated to reduce particulate matter in the stack gas. Any number of additional discharge improvements can be implemented but they are generally not implemented unless one has a dynamic sample derived from the discharge.
It is not uncommon to connect a stack directly from a furnace or smelting operation so that the gases from the combustion chamber are discharged directly into the stack. In fact, the gases entering the stack may be at substantially elevated temperatures. The stack is normally constructed of firebrick and a similarly fire resistant lining is included at the lower portions of the stack. In fact, the fire brick and lining may extend practically the full length of the stack. A stack tends to draw dependent on scale factors including stack height. Velocities may be negligible in the lower portions of the stack and especially near the furnace. By contrast, the discharge gases travel quite rapidly as a result of buoyant forces as they approach the top of the stack. The hot gas discharge is lighter than the ambient atmosphere as a result of heating. This stream of hot gases typically accelerates as it approaches the top end of the stack. Many stacks are built as tall as 600 feet so that the discharge is substantially cooled and is much more homogenous in nature at the top of the stack. Afterburning to the extent that it might occur in the firebox or furnace discharge and while rising in the stack, is substantially complete so that the gases discharged to atmosphere can be captured best only at the top portions of the stack. Accordingly, the stream of discharge gases from the stack is best sampled at the top of the stack.
It is possible to derive a sample from lower regions of the stack, but it is questionable whether or not such a sample will represent the actual discharge to atmosphere. For that reason, the stack discharge is best sampled at the top of the stack. Moreover, entry into the stack interior is more readily accomplished at the top where the discharge is cooler, after-burning has substantially been completed, and the stream is more thoroughly mixed. For flare, vent or blow down stacks the gas product flowing to the top of the stack moves through a line when a valve is opened to vent gases through a flare into the atmosphere. To confirm to the governing agencies that the gases vented are not banned, the present apparatus is a system best installed near the top of the stack for collecting a sample. The system incorporates a protruding probe having an opening at the end thereof which is positioned approximately along the stack's center line near the top end to take a sample of the discharge from the stack. The sample is quite small compared to the volume of gases flowing through the stack. Stacks presently exist which discharge over 1,000 tons of hot gases daily; while such a flow rate is extraordinarily large, the sample is extraordinarily small compared with the total flow. The sample is much smaller than one part in a hundred, indeed, is about one part in 10.sup.6 or 10.sup.8. Even then, that sample which is delivered to the apparatus of the present disclosure may be quite large and must be reduced in size again as will be discussed.
The present disclosure is directed to a sample system which incorporates an inlet installed in a stack for obtaining a sample. This sample is delivered along a small line on the stack to the sample measuring apparatus of the present disclosure. The large sample is further metered through a system which reduces the size of the sample or specimen even further. This step again reduces the size of the sample in contrast with the stack discharge by another two, three or four orders of magnitude so that the sample size to the stack discharge can be controllably scaled to be as large as one part per 10.sup.5 down to one part in 10.sup.10. Indeed, even smaller samples can be taken as desired by serially connecting additional sample removing means.
It is important that a sample be truly representative. To this end, the present apparatus sets forth a timed sampling system which operates periodically, preferably in proportion to the flow through the stack and perhaps once per hour, once per minute, once per ten seconds, etc. Samples taken at a controlled time rate are delivered into a storage container so that the storage container cumulatively stores a continuous sample flow preparatory to testing by the operator. This stored sample is thus proportionate to the discharge of the stack for the collection time interval. Assume that the collected samples are derived from a ten day period. In that instance, the storage container is provided with the intended proportionate specimen collected over ten days. The sample collected in ten days thus should provide a precise analysis of the stack discharge over the ten day interval. It can be taken conveniently to a laboratory for testing for constituents including SO, SO.sub.x, NO, NO.sub.x, CO, and any other discharge from the stack.
The present apparatus thus takes advantage of the height of a stack. The sample is more like the actual atmospheric discharge at the top end of the stack. Moreover, the afterburning which might be involved in the lower portions of the stack is substantially complete by the time the discharge gases reach the top of the stack. Another benefit is that mixing and commingling occurs so that the sample is more true to the effluent flow in the stack. Last of all, it is not necessary to attempt to enter the stack at the lower regions typically made of materials which are difficult to penetrate, namely an inside liner and firebrick. The liner is normally formed of ceramic materials which are difficult to work with. This device permits the installation of equipment operative at lower temperatures.
The apparatus of this disclosure is a system which can be installed with an intake at or near the top of a smoke stack, and which incorporates a sample line extending down the stack to equipment located at or near the ground at the base of the smoke stack. Equipment includes a constant pressure storage cylinder which has an internal piston which moves to provide a chamber for storage of the sample. The equipment also includes apparatus which proportions the sample and delivers it at a controlled rate for storage. The timing may be interfaced with measurement to provide a sample taken proportional to the flow in the line or out the stack. A timer operates a solenoid valve which periodically is switched off and on to provide timed operation to a diaphragm powered plug cutting apparatus which cuts a plug from the sample flow from the stack. In addition, there is an aspirator which is driven by a supply of compressed air for the purpose of forcing surplus sample into a stack return line which is extended along the stack and which empties at the common fitting supporting the inlet at the top of the stack.